This invention relates generally to the field of fabric tension measurement and more specifically to the measurement of the propagation velocity of an acceleration wave in fabric under tension enabling the tension to be calculated based upon the velocity.
Fabric is typically constructed having a plurality of parallel warp threads running the length of the fabric in which is interwoven a plurality of perpendicular fill threads. The threads can be made from a variety of materials including thermoplastic strands. The fabric may be treated or coated to impart certain desirable characteristics.
In certain applications it may be desirable to utilize fabric as a structural element by stretching the fabric over a framework to cover an expanse such as in a tent construction. When fabric is placed under tension, it is desirable to know the vector tension existing in the warp and fill directions to determine the forces acting on the fabric. In applications where the forces acting upon the fabric can be controlled, such as in a tent, the fabric tension can be adjusted to a safe operating value. In applications where the forces acting upon the fabric cannot be conveniently controlled, it is still important to know the tension in order to determine if the fabric is operating within safe limits and to determine what additional loading could be safely accommodated. Therefore, it will be apparent that there exists a need for an apparatus which can accurately measure warp and fill tension in stretched fabric constructions.
The tension in stretched fabric can be calculated from the equation F=V.sup.2 D, wherein F is the tension (force) per unit length, V is propagation velocity of an acceleration wave in the fabric in either the warp or fill direction, and D is the density per unit area of the fabric. Since the density per unit area of the fabric can be easily determined, only the measure of the velocity poses a problem. It should be noted that the above equation is valid only for the propagation velocity of an acceleration wave, such as produced by an acceleration discontinuity in the fabric, along the warp or fill axes.